What kind of instruments generally show the height of airspace above ground level?

The correct answer highlights that standard altimeters are specifically designed to measure altitude based on atmospheric pressure, which corresponds to the height of the aircraft above a predefined pressure level, typically mean sea level. Standard altimeters are calibrated to reference the standard atmospheric pressure at sea level, and they provide pilots with critical information about their altitude as they fly, including how high they are relative to the terrain beneath them.

In aviation, standard altimeters display height in feet above mean sea level (MSL), which is essential for maintaining safe vertical separation from the ground and other aircraft. When transitioning from one location to another, pilots often adjust their altimeter settings based on local barometric pressure to ensure accurate altitude readings.

Radar altimeters, on the other hand, measure height above the terrain directly using radio waves, providing precise altitude information primarily during the approach and landing phases, but not as a general reference for altitude in all phases of flight.

Vertical speed indicators provide information about how fast an aircraft is climbing or descending, not the actual altitude. Pressure altimeters, while related to standard altimeters, typically do not refer to the ground level specifically, as they might use different settings or reference points that make them less suitable for determining the height of airspace above ground level.